Not a Visual Studio issue - it's an OS WOW64 bug.
However, since there's no way to report a bug against the OS (why is that???), it's been suggested to me by Michael Sun (of Microsoft) to report it here.
The issue is described here: http://social.msdn.microsoft.com/Forums/en-US/windowscompatibility/thread/1558e9ca-8180-4633-a349-534e8d51cf3a
and here: http://zachsaw.blogspot.com/2010/11/wow64-bug-getthreadcontext-may-return.html
To obtain the 32-bit app in question, pls contact Michael. Get the debug version.